It has long been known that the triphenylmethane dyes, which are triphenylmethane derivatives containing at least one auxochromic group, such as amino, para to the central methane carbon atom, form leuco cyanides which in the presence of certain activators become photosensitive to ultra-violet and shorter wave lengths of photons to produce colored compounds but which are not sensitive to light in the visible range. It is also well known, as disclosed in U.S. Pats. No. 2,855,303 and No. 3,306,748, that various film-forming hydrocolloids or polymers may be used as activators for triphenylmethane dye cyanides. Such thin films have been produced and used in the area of radiation dosimetry. Until the present work, the solid activator matrix that best sensitized radiolytic dye production was gelatin. Gelatin, however, has the serious problems of dimensional instability and migration of the dye formed after irradiation.
Furthermore, while thin films of these triphenylmethane dye cyanides have been used successfully for accurate determination of one- and two-dimensional depth-dose distributions in various high-Z and low-Z materials and multilayer absorbers using high absorbed doses of x-and gamma rays and electrons, these films cannot successfully be used for studying three-dimensional dose distributions in solid media. For example, when a three centimeter-thick gelatin matrix incorporating the dye cyanide is used to determine doses of greater than 10.sup.3 rads, it is observed that the gelatin undergoes shrinkage after setting and exhibits poor dimensional stability and a tendency for the dye to diffuse into the medium after irradiation. Accordingly, there is a need in the art for the development of a more mechanically stable solid system in which the desirable dosimetric characteristics of the dye cyanide are preserved and in which the dye cyanide is more sensitive to radiation.
It should be understood that while it is known that such dye cyanides may be activated in polyvinyl pyrrolidone systems as disclosed in U.S. Pat. No. 3,306,748, these systems can only be cast as thin films because they are formed by dissolving the dye cyanide into a solution of the polymer.